Hey Gina!
I'm also a hypo. I was as a child and was able to beat it as a teenager only to have it come back in my 20s. And now I've been dealing with it for the last 12 years. I don't know why it happens, but I don't think the why is as important as learning to let it go. One thing that helps me when I'm having a hypo moment and determined I'm dying of some disease is telling myself that I am healthy and everything is ok and that if something wasn't ok, I would have help by going to the doctors. I used to take the bus to work and I would panic just knowing I was going to be trapped on that bus having a heart attack or something. I realized one day that if something were to happen, the people on the bus wouldn't let me die on the bus because it's human nature to help people in trouble. Human nature for probably 90% of people anyway - there are very mean people out there who don't care about anone or anything so I can't say it's human nature for all people. But, my point is that if something was wrong, you would have help.
Another thing that helps me is to remind myself that not paying attention to my vitals is not going to make something happen. I have a terrible habit of checking my pulse rate. I started to challenge myself to not check my heart rate all day no matter what. By doing that, I was able to prove to myself that the human body knows how to keep itself going (by absolute brilliant design) and you don't need to constantly pay attention to every skipped heart beat or ache and pain. How many times have you been sick and not died? How many times has your heart took off racing when you felt it shouldn't and didn't keal over? I know it's hard but try to trust your body. I still struggle with this but after trying to remind myself to do these things, it is getting easier to let things go that would've set me off before.
Sorry that was so long winded and preachy. I hope it helps!